Various kinds of automatic regulating valve devices have been proposed. A lift valve apparatus disclosed in JP-B No. 2-46818 is a direct-acting constant-flow valve not provided with any pilot valve.
As shown in FIG. 23, this prior art lift valve apparatus has a valve casing 101 having an internal space divided into three passages, i.e., an inlet passage a an intermediate chamber u and an outlet passage c arranged in that order from an upstream side toward the downstream side, by a flow rate setting valve element 103 and an automatic restriction control valve element 104. The respective pressure receiving areas of the valve element 103 and the automatic valve element 104 are substantially equal. A sealed chamber e defined by a sealing member 104s attached to the automatic valve element 104, and a valve top 102 is connected to the inlet passage a by a connecting passage t. The automatic valve element 104 is biased for automatic restriction control function by a balancing spring 105. The automatic valve element 104 moves automatically in opposite directions according to the position of the valve element 103 corresponding to a set opening to maintain a constant flow rate.
This direct-acting constant-flow valve is used prevalently. However, the direct-acting constant-flow valve has unsolved problems in forming the same in large size and high-pressure type. The size of the balancing spring 105 increases inevitably as the size and the pressure capacity of the direct-acting constant-flow valve are increased, entailing difficulties in assembling, designing and manufacturing the direct-acting constant-flow valve. It is not easy to select a balancing spring 105 capable of properly controlling flow rate in a conduit in which pressure varies frequently.
Pilot-operated automatic regulating valve apparatuss provided with a main valve driving piston or diaphragm operated by a pilot valve, which adjusts flow rate with a fixed restriction passage such as a needle valve, are also used prevalently instead of the direct-acting constant-flow valve. A liquid level control valve provided with a float valve as a pilot is one of those valve apparatuses.
Referring to FIG. 24, this liquid level regulating or control valve apparatus has a main valve unit controlled by the opening and closing actions of a piloting float valve 230. The main valve unit has a main valve casing 201, a main valve element 205 disposed in the main valve casing 201, and a main valve driving member 206 having a pressure receiving area greater than that of the main valve element 205 and combined with the main valve element 205. A restricted passage is formed between the main valve element 205 and a main valve seat 204. The main valve driving member 206 is fitted slidably in a space defined by a cylindrical wall 203 formed inside the main valve casing to form a main valve driving pressure chamber d between the cylindrical wall 203 and a valve top 202. The float valve 230 closes when the liquid level on the downstream side of the main valve unit rises above a predetermined level and opens when the same drops below the predetermined level. The main valve driving pressure chamber d is connected to an inlet passage in an upstream end of the main valve unit by a connecting passage t provided with a fixed restricting valve 220 and is connected through the float valve 230 to the downstream side of the main valve unit. The pressure in the main valve driving pressure chamber d drops to the pressure in a passage on the downstream side of the main valve unit when the float valve 230 opens, and the main valve element 205 is moved in a valve opening direction to start supplying the liquid. In the meantime, the float valve 230 closes when the liquid level on the downstream side of the main valve unit rises above the predetermined level, the pressure in the main valve driving pressure chamber d rises to the pressure on the upstream side of the main valve unit, and the main valve element 205 is moved so that a sealing member 205s comes into close contact with the main valve seat 204 to stop supplying the liquid.
This prior art pilot-operated automatic regulating valve apparatus, however, needs troublesome maintenance and management work and has many problems in durability. The following are examples of those problems.
(1) Most of various sealing means for use as a sealing member 206s put on the main valve driving member 206 in contact with the cylindrical wall 203 are required to achieve perfect sealing not permitting leakage when the main valve unit is closed, and a bellows and a diaphragm have been employed as the sealing member 206s to solve the problem. When the pilot-operated automatic regulating valve apparatus is of a large size and a large pressure capacity, difficulties arise in the durability and machining accuracy of the sealing arrangement, and troublesome maintenance and management work is necessary; that is, the fluid is liable to leak downstream.
(2) The main valve unit must gradually be driven to prevent undesirable operations, such as chattering and hunting, due to pressure pulsation resulting from the change of flow. Therefore, the prior art pilot-operated automatic regulating valve apparatus needs the fixed restricting valve 220 forming a restricted passage, such as a needle valve, in the connecting passage t through which the fluid of the upstream pressure flows. This small restricted passage is clogged with sand and dust to cause troubles and hence a strainer or the like is necessary. Thus, it is difficult to use this prior art pilot-operated automatic regulating valve apparatus in fluid passages other than a fluid passage for a clean liquid.
The present invention employs a pilot valve unit based on a novel technical idea to realize a valve capable of being formed in a large size and a large pressure capacity, which could not have been realized by the prior art direct-acting constant-flow valve. Also, it is an object of the present invention to provide a pilot-operated automatic regulating valve apparatus capable of exercising excellent automatic control functions including a constant-flow control function, an emergency shutoff function, a liquid level control function and an upstream pressure control function, having a perfect sealing function, provided with a pilot valve unit not having any fixed restricting passage, such as a needle valve, and capable of exercising a clogging preventing function achieved by self-cleaning operation, capable of operating quickly without entailing chattering and hunting, and convenient for application.